1. Field of the Invention
The present invention relates to a controller for a machine tool where the tool replacing control can be carried out when oil mist for internal oil supply and a center through coolant are both used in a cutting process using a machine tool.
2. Description of the Related Art
Japanese Unexamined Patent Publication H2 (1990)-250702 discloses a cutting method according to which a coolant is directly supplied to the edge from a through hole (which is referred to as an oil hole) at the tip of the tool through a center through main axis in a cutting process using a machine tool, which is generally referred to as a center through process. Center through processes make it possible to dramatically increase the coolability and the lubricity at the cutting point, and as shown in WO98/23384, an oil mist is supplied through the pipe of the center through main axis so as to supply the oil mist to the edge instead of a coolant, depending on the machine tool.
Meanwhile, Japanese Unexamined Patent Publication 2007-290113 (turret type tool replacing unit in FIG. 2 (d)) and Japanese Unexamined Patent Publication 2008-296322 (swing arm type tool replacing unit in FIG. 10) disclose an example of a tool replacing unit equipped in a machine tool.
In the case where a coolant and an oil mist are both used and pass through the same pipe, the coolant remaining within the pipe is first discharged from the through hole at the tip of the tool when the oil mist is discharged, and thus, such a problem arises that a coolant is used for the process irrelevant of the fact that the cutting requires oil mist.
In many cases, the cutting conditions when an oil mist is used are different from the conditions for processing when a coolant is used, and therefore, processing in the state where a coolant is being discharged from the pipe under the cutting conditions for the use of an oil mist (cutting conditions that are not suitable for a coolant) results in damage to the edge.
In order to solve this problem, the prior art provides a technique for putting the process in a stand-by state for a certain period of time until the remaining coolant has been discharged. However, the remaining coolant is discharged over a long period of time depending on the length of the pipe and the diameter of the oil hole of the tool, which makes the stand-by state last over a long period of time.